One Transistor Fixed Power Supply 6/9/12 V x 500 mA or 1 A (ART326E)

Using a single transistor as a regulator and having a zener diode as a reference, we can design a simple yet efficient source to power 6 to 12 V appliances with currents up to 1 A, depending on the version chosen.

We present a 6, 9 or 12 V fixed power supply design with 500 mA or 1 A current that can be used to power small electronics such as AM / FM radios, toys, small keyboards, etc. The circuit is regulated which provides excellent performance for many powered devices, unlike those disposed of conventional batteries that mostly do not have regulation.

How it works

In this circuit, the transformer lowers the voltage of the power grid, which is rectified by D1 and D2, and then filtered by the electrolytic capacitor. The regulation is done by a step containing a zener diode and a power transistor. In function of these components and the resistor R1 we have the output voltage and the maximum current, according to the following table:

Output voltage

Current (ma)

Transistor o

Zener

Resistor R1

Transformer

6 V

500 mA

BD135/137/139

6 V x 400 mW

270 ohm x 1 W

7,5 + 7,5 V x 500 mA

6 V

1 A

TIP31A/B/C

6 V x 400 mW

220 ohm x 1 W

7,5 + 7,5 V 1 A

6 V

500 mA

BD135/136/137

6 V x 400 mW

330 ohm x 1 W

9 + 9 V x 500 mA

6 V

1 A

TIP31/A/B/C

6 V x 400 mW

270 ohm x 1 W

9 + 9 V x 1 A

6 V

500 mA

BD135/137/139

6 V x 400 mW

470ohm x 1W

12 + 12 V x 500 mA

6 V

1 A

TIP31/A/B/C

6 V x 400 mW

390 ohm x 1 W

12 + 12 V x 1 A

9 V

500 mA

BD135/136/137

9V1 x 400 mW

220 ohm x 1 W

9 + 9 V x 500 mA

9 V

1 A

TIP31/A/B/C

9V1 x 400 mW

150 ohm x 1W

9 + 9 V x 1 A

9 V

500 mA

BD135/136/137

9V1 x 400 mW

220 ohm x 1 W

12 + 12 V x 500 mA

9 V

1 A

TIP31/A/B/C

9V1 x 400 mW

270 ohm x 1 W

12 + 12 V x 1 A

12 V

500 mA

BD135/136/137

12 V x 400 mW

220 ohm x 1 W

12 + 12 V x 500 mA

12 V

1 A

TIP31/A/B/C

12 V x 400 mW

180 ohm x 1W

12 + 12 V x 1 A

In all cases, if a transformer with secondary current less than the expected maximum is used, this will be the current obtained from the source.

Assembly

In figure 1 we have the complete diagram of this source.

Figure 1 - Complete diagram of the power supply

There are several techniques that can be used for assembly. If printed circuit board is used, the pattern of Figure 2 may serve as a basis.

Figure 2 - Printed circuit board for the assembly of the source.

Capacitor C1 must have a working voltage of at least 50% than the secondary voltage of the transformer used. The transistor must be provided with a good heat radiator. Note that the terminal arrangement of the BD series transistors is different from the TIP series.